U.S. patent application number 13/825001 was filed with the patent office on 2013-10-31 for system intended to reduce the amount of nox in the exhaust gases of a motor vehicle.
This patent application is currently assigned to AAQIUS & AAQIUS S.A.. The applicant listed for this patent is Arnaud Audouin, Jean-Baptiste Dementhon. Invention is credited to Arnaud Audouin, Jean-Baptiste Dementhon.
Application Number | 20130287656 13/825001 |
Document ID | / |
Family ID | 43640033 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130287656 |
Kind Code |
A1 |
Audouin; Arnaud ; et
al. |
October 31, 2013 |
SYSTEM INTENDED TO REDUCE THE AMOUNT OF NOX IN THE EXHAUST GASES OF
A MOTOR VEHICLE
Abstract
The invention relates to a system intended to reduce the amount
of NOx in the exhaust gases of a motor vehicle. The system
comprises a storage space (1) containing a reducing agent; an SCR
(selective catalytic reduction) catalytic converter (5) for
treating the exhaust gases laden with reducing agent, and an
injection module (6c) designed to inject the reducing agent from
the storage space (1) into the exhaust gases of the motor vehicle
upstream of the SCR catalytic converter (5). The system further
comprises: at least one heat exchanger (2) connected to the storage
space (1) and containing a porous matrix intended to absorb the
reducing agent originating from the storage space (1); a valve or
an injector (11) downstream of the storage space (1) and upstream
of the exchanger (2) and designed to control the addition of
reducing agent to the exchanger (2), and a valve (12) positioned
between the storage space (1) and the exchanger (2). This is
designed to transfer thermal energy to the exhaust gases of the
motor vehicle upstream of the SCR catalytic converter (5) during a
first period known as the starting period following the starting of
said vehicle. The valve or the injector (11) is designed to control
the rate of flow of reducing agent into the exchanger (2) during
said starting period so that the absorption of the reducing agent
by the porous matrix of the exchanger (2) raises the temperature
thereof. The valve or the injector (11) is also designed then to be
closed during a period known as the period at operating temperature
when the motor vehicle is running as soon as the exhaust gases have
reached a certain temperature. The valve (12) is designed firstly
to regulate the pressure inside the exchanger (2) during said
period at operating temperature and secondly to convey the reducing
agent contained in the exchanger (2) to the storage space (1) when
the pressure inside the exchanger (2) is higher than the pressure
inside the storage space (1).
Inventors: |
Audouin; Arnaud; (Paris,
FR) ; Dementhon; Jean-Baptiste; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Audouin; Arnaud
Dementhon; Jean-Baptiste |
Paris
Paris |
|
FR
FR |
|
|
Assignee: |
AAQIUS & AAQIUS S.A.
Geneve
CH
|
Family ID: |
43640033 |
Appl. No.: |
13/825001 |
Filed: |
October 20, 2011 |
PCT Filed: |
October 20, 2011 |
PCT NO: |
PCT/IB2011/002522 |
371 Date: |
June 5, 2013 |
Current U.S.
Class: |
423/212 ;
422/109; 422/169; 422/172; 422/173 |
Current CPC
Class: |
F01N 3/0205 20130101;
Y02T 10/12 20130101; F01N 3/2066 20130101; F01N 2570/18 20130101;
Y02T 10/22 20130101; F01N 2240/02 20130101; F01N 2610/02 20130101;
F01N 2610/06 20130101; Y02T 10/24 20130101; F01N 3/0871 20130101;
B01D 53/9431 20130101; Y02A 50/2325 20180101 |
Class at
Publication: |
423/212 ;
422/169; 422/172; 422/173; 422/109 |
International
Class: |
B01D 53/94 20060101
B01D053/94 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2010 |
EP |
10013919.5 |
Claims
1. System intended to reduce the quantity of NOx in the exhaust
gases of a motor vehicle, the system comprising: a storage chamber
containing a reducing agent; an SCR (Selective Catalytic Reduction)
catalyst for treating the exhaust gases loaded with reducing agent,
and an injection module arranged to inject the reducing agent
coming from the storage chamber into the exhaust gases of the motor
vehicle, upstream of the SCR catalyst, wherein said system also
comprises: at least one heat exchanger connected to the storage
chamber and containing a porous matrix intended to absorb the
reducing agent coming from the storage chamber; a shutter or
injector downstream of the storage chamber and upstream of the
exchanger and arranged to control the addition of reducing agent in
the exchanger, and a valve placed between the storage chamber and
the exchanger; and wherein the exchanger is arranged to transfer
thermal energy to the exhaust gases of the motor vehicle upstream
of the SCR catalyst during a first so-called starting period
following the starting of said vehicle; the shutter or injector is
arranged to control the flow rate of reducing agent in the
exchanger during said starting period so that the absorption of the
reducing agent by the porous matrix of the exchanger raises the
temperature of the latter; the shutter or injector is arranged then
to be closed during a so-called operating-temperature period during
the functioning of the motor vehicle as soon as the exhaust gases
have reached a certain temperature; and the valve is arranged so as
firstly to regulate the pressure in the exchanger during said
operating-temperature period and secondly to convey the reducing
agent contained in the exchanger into the storage chamber when the
pressure in the exchanger is greater than the pressure in the
storage chamber.
2. System according to claim 1, wherein the shutter or injector is
arranged to be closed right from the start of the
operating-temperature period of the motor vehicle until the
beginning of the next starting period.
3. System according to claim 1, wherein it also comprises a heating
body arranged to heat the storage chamber according to the value of
one or more parameters chosen from the concentration of emitted
NOx, the temperature of the engine lubricant, the temperature of
the engine cooling liquid, the speed of the vehicle, the engine
speed and the engine load.
4. System according to claim 1, wherein the reducing agent is
ammonia.
5. System according to claim 4, wherein the storage chamber
contains pressurised ammonia and in that the porous matrix of the
exchanger is a salt chosen from metal chlorides such as barium
chloride, strontium chloride, magnesium chloride, calcium chloride
and nickel chloride.
6. System according to claim 4, wherein the storage chamber and the
exchanger contain respectively first and second salts, the salts
being metal chlorides chosen so that the ammonia desorption
enthalpy of the first salt is less than the ammonia desorption
enthalpy of the second salt.
7. System according to claim 1, wherein the exchanger is arranged
in the exhaust gases downstream of a module for injecting the
reducing agent and upstream of the SCR catalyst.
8. System according to claim 1, wherein it also comprises one or
more additional cleanup elements chosen from an oxidation catalyst,
a three-way catalyst and a particulate filter, the cleanup element
or elements being arranged upstream from the module for injecting
the reducing agent whereas the SCR catalyst is arranged downstream
of said injection module, and in that the exchanger is arranged
upstream of said additional cleanup element or elements.
9. System according to claim 8, wherein the porous matrix of the
exchanger or exchangers or are disposed inside a tube around the
exhaust pipe upstream of the SCR catalyst and/or upstream of said
additional cleanup element or elements.
10. System according to claim 8, wherein the porous matrix of the
exchanger or exchangers is or are disposed around the SCR catalyst
and/or around said additional cleanup element or elements.
11. System according to claim 1, wherein it also comprises a pipe
for recirculating the exhaust gases (hereinafter referred to as
EGR), a tube mounted around the EGR pipe, the difference in
diameter between the tube and the EGR pipe creating a volume inside
which the porous matrix of the exchanger is arranged so as to be
able to cool the EGR gases by conveying the reducing agent from the
storage chamber to the exchanger when the temperature of the gases
circulating in said EGR pipe exceeds a critical threshold.
12. Motor vehicle comprising the system according to claim 1,
wherein the vehicle comprises a turbocompressor the turbine of
which is arranged downstream of the exchanger.
13. Method of implementation of the system according to claim 1,
comprising the following steps: opening the shutter or injector
when the motor vehicle is started so that the reducing agent
contained in the storage chamber is conveyed in gaseous form into
the exchanger under the effect of the pressure difference existing
in respectively the storage chamber and the exchanger; closing the
shutter or injector when the temperature of the gases has reached a
predetermined value; progressively draining the exchanger during
the operating-temperature period of the motor vehicle, by
discharging the reducing agent through the valve so that it is once
again introduced into the storage chamber.
14. Method according to claim 13, in which the exchanger is
completely drained and does not contain any reducing agent at the
time of starting of the motor vehicle.
15. Method according to claim 13, in which the opening the shutter
or injector is controlled by a computer according to the value of
one or more parameters chosen from the concentration of emitted
NOx, the temperature of the engine lubricant, the temperature of
the engine cooling liquid, the exhaust temperature in the gas
stream or inside the catalyst channels or filters, the speed of the
vehicle and the engine speed.
16. Method for using the system according to claim 8, in which the
shutter or injector is open when the motor vehicle is started so
that the reducing agent contained in the storage chamber is
conveyed in gaseous form into the exchanger arranged upstream of
the oxidation catalyst in order to promote the production of
NO.sub.2 by the latter so as to improve the activation of the SCR
catalyst.
17. Method of implementation of the system according to claim 12,
in which the shutter or injector is open when the motor vehicle is
started so that the reducing agent contained in the storage chamber
is conveyed in gaseous form into the exchanger in order to
accelerate the actuation of the turbine, and in which the shutter
or injector is closed when the temperature upstream of the turbine
exceeds the normal operating temperature range of the turbine.
Description
[0001] The proposed invention relates to an SCR (Selective
Catalytic Reduction) catalyst system intended to reduce the
quantity of NOx in the exhaust gases of a motor vehicle.
[0002] Emissions of pollutants related to transport have for around
thirty years been a prime dynamic of progress in industry. The fact
that the emission limits for the four regulated pollutants (CO, HC,
NOx, particulates) have progressively become more severe has
significantly enabled improvement in air quality, in particular in
large towns.
[0003] The ever increasing use of motor cars requires pursuing
efforts for reducing these emissions of pollutants still further.
Thus the reduction of nitrogen oxides (NOx) remains a complex
problem in the context of the more severe European emission
thresholds expected in 2015 with the coming into force of the 6
standard. Having available pollution control technologies that are
highly effective under all running conditions remains a major
challenge for the transport industry.
[0004] Secondly, the consumption of fuel, in direct relationship
with CO.sub.2 emissions, has become in few years the major concern
for the car industry. Thus, regulations will be put in place at a
European level as from 2012 on the CO.sub.2 emissions of private
cars. It is already established that this limit will be regularly
lowered over the decades to come. CO.sub.2 is therefore imposed as
the new growth driver for the whole transport industry.
[0005] This double problem of reduction of local pollution (NOx)
and reduction in fuel consumption (CO) is particularly difficult
for the diesel engine, the combustion of which in a lean mixture is
accompanied by a NOx emission that is difficult to deal with.
[0006] It is in this context that the SCR post-treatment technology
is envisaged both for vehicles allocated to goods transport and
private vehicles. It has in fact been demonstrated that the high
efficiency of NOx reduction makes it possible to position the
engine on its optimum functioning in terms of efficiency, the high
NOx emissions then being treated at the exhaust by the SCR
system.
[0007] One constraint of the SCR technology is the need to install
on a vehicle a reducing agent necessary for the reduction of the
nitrogen oxides. The system currently adopted for heavy goods
vehicles uses urea in aqueous solution as the reducing agent.
Injected in the exhaust, the urea decomposes into ammonia
(NH.sub.3) through the effect of the temperature of the exhaust
gases and enables the NOx to be reduced on a specific catalyst.
[0008] The integration of a reservoir of urea in aqueous solution
remains a high constraint for the SCR system. An alternative
solution under study is the storage of gaseous ammonia in salts. In
this case, the ammonia is stored in the form of a chemical complex
in a porous matrix consisting in particular of salts of the
chloride type (MgCl.sub.2, SrCl.sub.2, CaCl.sub.2, BaCl.sub.2,
ZnCl.sub.2, etc.). The ammonia is desorbed by modifying the
temperature and/or pressure of the matrix and is then injected into
the exhaust for treatment of the NOx.
[0009] The chemical reactions involved in the post-treatment of
fumes coming from combustion within thermal engine are catalytic
reactions that depend principally on the temperature of the exhaust
gases and the catalytic impregnation.
[0010] However, when the vehicle is started up, the temperature of
the exhaust gases is insufficient to provide significant catalytic
conversion. It is therefore necessary to wait for a certain length
of time for the exhaust gases to reach a temperature at which the
reduction of the NOx by SCR is effective. FIG. 1 shows a typical
change in exhaust temperature over a Europe approval cycle (New
European Driving Cycle: NEDC). The NOx emissions obtained after
post-treatment by the SCR catalyst and the efficiency of this
post-treatment are also indicated. Thus, when the vehicle starts,
the temperature in the exhaust is insufficient to ensure
significant catalytic conversion, the emissions issuing from the
engine are therefore not post-treated, and efficiency is close to
zero. The temperature progressively increases during the cycle and
then enables "ignition" of the post-treatment system, and catalytic
conversion is possible with an efficiency that may approach
100%.
[0011] The aim of the present invention is therefore to provide a
system intended to reduce the quantity of NOx in the exhaust gases
of a motor vehicle and arranged to accelerate the temperature rise
of the exhaust gases when the motor vehicle starts in order to
shorten the time necessary for the catalytic conversion to be
optimum.
[0012] In accordance with the invention, this aim is achieved by
virtue of an SCR catalyst system intended to reduce the quantity of
NOx in the exhaust gases of a motor vehicle, the system comprising:
a storage chamber containing a reducing agent; an SCR catalyst for
treating the exhaust gases loaded with reducing agent, and an
injection module arranged to inject the reducing agent coming from
the storage chamber into the exhaust gases of the motor vehicle,
upstream of the SCR catalyst. The system according to the invention
also comprises: at least one heat exchanger connected to the
storage chamber and containing a porous matrix intended to absorb
the reducing agent coming from the storage chamber; a shutter or
injector downstream of the storage chamber and upstream of the
exchanger and arranged to control the addition of reducing agent in
the exchanger, and a valve placed between the storage chamber and
the exchanger. The exchanger is arranged to transfer thermal energy
to the exhaust gases of the motor vehicle upstream of the SCR
catalyst during a first so-called starting period following the
starting of said vehicle. The shutter or injector is arranged to
control the flow rate of the reducing agent in the exchanger during
said starting period so that the absorption of reducing agent by
the porous matrix of the exchanger raises the temperature of the
latter. The shutter or injector is also arranged then to be closed
during a so-called operating-temperature period during the
functioning of the motor vehicle as soon as the exhaust gases have
reached a certain temperature. The valve for its part is arranged
so as firstly to regulate the pressure inside the exchanger during
said operating-temperature period and secondly to convey the
reducing agent contained in the exchanger into the storage chamber
when the pressure inside the exchanger is greater than the pressure
inside the storage chamber.
[0013] In a preferential embodiment of the invention, the storage
chamber contains a first salt while the exchanger contains a second
salt. The salts are metal chlorides chosen so that the ammonia
desorption enthalpy of the first salt arranged in the storage
chamber is less than the ammonia desorption enthalpy of the second
salt arranged in the exchanger.
[0014] In another embodiment of the invention, the storage chamber
comprises pressurised ammonia as reducing agent instead of the
first salt.
[0015] The invention also relates to a method for implementing the
SCR catalyst system comprising the following steps: [0016] opening
the valve when the motor vehicle starts so that the reducing agent
contained in the storage chamber is conveyed in gaseous form in the
exchanger under the effect of the difference in pressure existing
in respectively the storage chamber and the exchanger; [0017]
closing the valve when the temperature of the gases has reached a
predetermined value; [0018] progressively draining the exchanger
during the operating period of the motor vehicle, by discharging
the reducing agent through the valve so that it is once again
introduced into the storage chamber.
[0019] The features of the invention will become more apparent from
a reading of the description of several embodiments, given solely
by way of examples, in no way limitatively, referring to the
schematic figures, in which:
[0020] FIG. 1 illustrates the efficiency of the catalytic
conversion, the NOx emissions and the temperature of the exhaust
gases according to an NEDC (New European Driving Cycle) approval
cycle for a conventional depollution system;
[0021] FIG. 2 illustrates an SCR catalyst system intended to reduce
the quantity of NOx in the exhaust gases according to a first
embodiment of the invention;
[0022] FIG. 3 illustrates an SCR catalyst system intended to reduce
the quantity of NOx in the exhaust gases according to a second
embodiment of the invention;
[0023] FIG. 4 shows a more detailed part of the system according to
the first and second embodiments of the invention;
[0024] FIG. 5 shows the operating principle of the system according
to the Clapeyron equation;
[0025] FIG. 6 shows the functioning of the heat exchanger in the
exhaust line according to the NEDC approval cycle;
[0026] FIG. 7 illustrates a schematic view of a cleanup element
with the exchanger arranged according to a first variant;
[0027] FIG. 8 illustrates a schematic view of a cleanup element
with the exchanger arranged according to a second variant;
[0028] FIG. 9 illustrates a schematic view of a gas recirculation
pipe around which the exchanger is arranged.
DETAILED DESCRIPTION OF THE INVENTION
[0029] In the system proposed, the storage of the reducing agent is
based on a reversible solid-gas reaction of the type:
##STR00001##
in which the gas is ammonia and the solid an anhydrous salt of the
metal chloride type: MgCl.sub.2, SrCl.sub.2, CaCl.sub.2,
BaCl.sub.2, ZnCl.sub.2, etc.
[0030] The absorption (i) and desorption (ii) reactions are
entirely reversible. The ammonia equilibrium pressure of the system
can be determined for a given temperature by the Clausius-Capeyron
equation that is given by the following formula:
ln P NH 3 = - .DELTA. Hr RT + .DELTA. Sr R ##EQU00001##
where .DELTA.Hr is the desorption enthalpy per mol of NH.sub.3,
.DELTA.Sr is the desorption entropy per mol of NH.sub.3 and R the
perfect gases constant.
[0031] According to this formula, the ammonia equilibrium pressure
of these salts depends on temperature.
[0032] According to the first embodiment of the invention as
illustrated by FIG. 2, the system comprises two composite materials
arranged respectively in the storage chamber 1 and in the exchanger
2. Each composite material comprises one or more compressed salts
and preferably expanded graphite, which is used as a binder so as
to obtain a porous matrix intended to receive ammonia. The salt of
the composite material arranged in the storage chamber 1
(hereinafter referred to as Salt A) and the salt of the composite
material arranged in the exchanger 2 (hereinafter called Salt B)
are chosen so that the ammonia desorption enthalpy of Salt A is
less than the ammonia desorption enthalpy of Salt B. Salt A is
preferably barium chloride (BaCl.sub.2) or strontium chloride
(SrCl.sub.2) while Salt B is preferably manganese chloride
(MnCl.sub.2), ferrous chloride (FeCl.sub.2) or magnesium chloride
(MgCl.sub.2).
[0033] With reference to FIG. 2, the storage chamber 1, containing
Salt A intended to absorb and desorb ammonia, is arranged to be
temperature-controlled by a heating body 3 in order to desorb the
ammonia from Salt A and convey it through a first pipe 4 in order
to be able to inject it into the exhaust gases upstream of an SCR
catalyst 5. To limit the consumption of energy of the heating body
3, the pressure inside the chamber 1 must be limited to a low value
while being sufficiently high to allow a sufficient flow of ammonia
compatible with the NOx emissions of the thermal engine. To this
end, the storage chamber 1 is connected to a supply module 6 that
is controlled by a dedicated computer 7 connected to the engine
computer 8. According to FIG. 4, this supply module 6 comprises a
device 6a for measuring the pressure or temperature in the storage
chamber 1 as well as an ammonia metering device 6b. The pressure or
temperature measured by the pressure or temperature measuring
device 6a in the chamber 1 is compared with a set pressure or
temperature. The latter is determined dynamically according to an
analysis of a certain number of engine and vehicle parameters, such
as for example the concentration of NOx emitted at each instant (a
quantity that can be measured and/or modelled), the temperature of
the engine lubricant, the temperature of the engine cooling liquid,
the temperature at the exhaust in the gas stream or in the catalyst
or filter channels, the speed of the vehicle, the engine speed, the
engine load or a combination of these parameters.
[0034] Still according to FIG. 2, the heat exchanger 2, connected
to the storage chamber 1 by a pipe 9, is arranged in the exhaust
gas flow downstream of one or more additional cleanup elements 10
in the form of an oxidation catalyst or a three-way catalyst and,
where applicable, a particulate filter, the heat exchanger 2 also
being arranged downstream of an ammonia injection module 6c and
upstream of the SCR catalyst 5.
[0035] According to FIG. 4, a valve 11 is mounted on the pipe 9
downstream of the storage chamber 1 and upstream of the exchanger
2, and is arranged so as to be controlled by the computer 7 so as
to control the addition of ammonia in said exchanger 2. The SCR
catalyst system according to the invention also comprises a valve
12 placed between the storage chamber 1 and the exchanger 2.
[0036] The functioning of the SCR catalyst system according to the
invention can be divided into two phases (FIG. 6), namely a first
starting phase beginning with the starting of the motor vehicle and
continuing until the exhaust gases have reached a temperature at
which the catalytic conversion is optimum (hereinafter referred to
as the starting period) followed by a second operating phase of the
motor vehicle continuing until the stopping of the engine
(hereinafter referred to as the operating period).
[0037] When the motor vehicle starts, the exhaust gases are
relatively cold. Under these circumstances, the temperature in the
storage chamber 1 is similar to that in the exchanger 2. Because of
the different natures of the salts A and B, the pressure inside the
storage chamber 1 is greater than the pressure inside the exchanger
2. During the starting period, the shutter 11 is open so that
ammonia in gas form is conveyed from the chamber 1 through the pipe
9 in order to be injected to in the exchanger 2 and absorbed by the
Salt B. This absorption causes an increase in the temperature of
the exchanger 2 in accordance with the Clausius-Capeyron equation,
enabling the exhaust gases to be heated by conduction of heat.
[0038] As soon as the exhaust gases have reached a temperature at
which the catalytic conversion is optimum, the valve 11 closes. The
temperature of the exhaust gases is then around 250.degree. C. or
even more, which raises the temperature of the exchanger 2, which
increases the pressure inside the latter. The valve 12 is arranged
firstly to regulate the pressure in the exchanger 2 during the
period at operating temperature and secondly to redirect the
ammonia from the exchanger 2 into the storage chamber 1. Thus,
under the effect of the temperature of the exhaust gases discharged
during the operating period of the motor vehicle, the exchanger 2
is progressively "emptied" of ammonia. During the operating
temperature period of the motor vehicle, the system according to
the invention functions in a completely passive way.
[0039] When the engine stops, the system returns gradually to the
outside temperature. Under these circumstances, the pressure in the
storage chamber 1 is once again greater than the pressure in the
exchanger 2. The shutter 11 is held in the closed position in order
to confine the ammonia gas in the storage chamber 1. The system is
regenerated, ready to function when the motor vehicle next starts
up.
[0040] In a second embodiment as illustrated by FIG. 3, the
additional cleanup element or elements (11) are arranged upstream
of the ammonia injection module 6c, whereas the SCR catalyst 3 for
its part is arranged downstream of the injection module.
[0041] In a second application of the present invention, the
metering device makes it possible to control the flow of ammonia
gas flowing to the exchanger 2 according to the pressure measured
in particular inside the storage chamber 1. This device of the
injector type then makes it possible to adjust the pressure rise
profile in the exchanger 2 and thus the heating capacity
transmitted to the exhaust gases.
[0042] According to a variant embodiment, the storage chamber 1
contains pressurised ammonia, instead of the Salt A, whereas the
exchanger 2 for its part contains a salt of the metal chloride type
such as barium chloride (BaCl.sub.2) or strontium chloride
(SrCl.sub.2).
[0043] In the present invention, the start and end of the exhaust
gas heating phase and the opening profile of the metering device
during this phase are controlled by a computer 7 according to a
certain number of engine parameters. The temperature of the engine
cooling water, the oil temperature, the temperature of the exhaust
gases and/or an analysis of the past and present running conditions
can in particular be taken into account. Through the calibration of
this control strategy, it is necessary to ensure that the
regeneration phase is sufficiently long and at a sufficiently high
temperature for the heating device to be fully regenerated before
the engine stops.
[0044] The principle described above provides a clever transfer of
ammonia between the storage chamber 1, which is intended to supply
firstly an injection system arranged in the exhaust line upstream
of the SCR catalyst 5, and secondly the exchanger 2, making it
possible to use the air-conditioning properties attached to the
chemisorption of the NH.sub.3 in a metal chloride allowing a
regulation of the exhaust temperature.
[0045] The exchanger 2 according to the invention is preferably
arranged as close as possible to the exhaust line. According to
FIG. 7, the porous matrix of the exchanger 2 is arranged around the
SCR catalyst 5 or any other cleanup element 10, the cleanup element
5, 10 and the porous matrix of the exchanger 2 being confined
inside a receptacle 13. In another configuration as illustrated by
FIG. 8, a tube 14 is arranged coaxially around the exhaust line 14'
at different points, the porous matrix of the exchanger 2 being
arranged in the space between the exhaust line 1' and the tube
14.
[0046] The porous matrix of the exchanger 2 can also be arranged
inside the catalyst 5 around the various catalytic slabs, this
arrangement further having the advantage of thermally insulating
the exhaust portions, including during the phases without ammonia
transfer, that is to say confining a maximum amount of heat inside
the exhaust and thus minimising the unnecessary energy losses to
the outside.
[0047] There exist several exhaust line architectures potentially
encountered on diesel engines, in particular: [0048] an
architecture comprising, following an exhaust gas recirculation
circuit (hereinafter "EGR pipe")-a turbine-an oxidation catalyst
(Diesel Oxidation Catalyst hereinafter "DOC"-a particulate filter
(Diesel Particulate Filter hereinafter "DPF")-NH.sub.3 injection
and an SCR catalyst. [0049] an architecture comprising, following
an EGR pipe-a turbine-a DOC-NH.sub.3 injection-an SCR catalyst-a
DPF, [0050] an architecture comprising, following an EGR pipe-a
turbine-a DOT-NH.sub.3 injection an SCR catalyst and a DPF on a
single substrate.
[0051] The aforementioned three architectures may also comprise a
second LP EGR pipe connection referred to as low pressure (LP "Low
Pressure" EGR in contradistinction to HP "High Pressure" EGR
present on all diesels), situated downstream of the DPF.
[0052] The exchanger 2 according to the invention can therefore be
arranged at different points according to the architecture and aim
sought. It could for example be arranged at any point upstream of
the turbine in order to accelerate the activation of the latter,
with a view to limiting "turbo lag" and thus increasing torque at
low engine speed. The reverse circulation (which makes it possible
to "empty" the exchanger 2), can be involved to extract the heat
from the exhaust line when the temperature exceeds the maximum
temperature tolerated by the turbine.
[0053] The exchanger 2 can also be arranged at any point upstream
of the oxidation catalyst (DOC) in order to accelerate the priming
of the SCR catalyst situated always downstream of the DOC. This
location can also have an impact for accelerating the activation of
the catalyst with a view to regenerating the particulate filter.
The storage capacity must fill during the phase where it is wished
to recover heat.
[0054] The exchanger 2 can also be arranged downstream of the
particulate filter in order to avoid overheating relating to the
regeneration of the particulate filter and thus protect the SCR
catalyst 5 from exotherms when it is situated downstream from the
filter. In this case, the storage chamber 1 must be emptied when it
is wished to prevent overheating.
[0055] The exchanger may also be arranged around the DPF substrate
when the SCR catalytic impregnation is situated at the filter in
order to avoid exotherms in the filtering material.
[0056] Finally, the exchanger may be arranged around the EGR pipes
(HP and BP) in order to promote the cooling of the EGR flows with a
view to increasing the flow rates thereof. In this case, the
storage chamber must be emptied when it is wished to cool the
EGR.
* * * * *